Dye dilution curves will be recorded in individual blood vessels in various parts of the ocular fundus. Data on the time of first appearance, time of peak concentration, mean transit time, and segmental flow in monkey and normal human fundi will be compared with those obtained under different physiological and pharmacological stimuli. Data will also be collected from patients with various systemic and ocular diseases. A new technique will be used for this purpose. It consists of multiple injections of minimal amounts of fluorescein or cardiogreen (one-fiftieth of the usual dosage) and continuous on-line recording of the dilution curve with a highly sensitive reflectometer built in our laboratory.